In recent years, as means for providing various materials (base materials) with surface modifications and functionality assignments, a surface graft polymerization method that graft-polymerizes a polymer on a surface of a base material has attracted attention. The method comprises two steps of (1) immobilizing a polymerization initiation group on the surface of the base material physically or chemically, and (2) performing a polymerization reaction beginning at the polymerization initiating group to produce a so-called polymer brush on the surface of the base material (for example, Patent Literature 1 and Patent Literature 2). The present invention relates to the technology corresponding to the step (1). Conventionally, in order to immobilize the polymerization initiating group on the surface of the base material, specific compounds having the polymerization initiating group have been applied to or adsorbed on the surface of the base material depending on the type of the base material.
For example, a silane coupling compound and a metal alkoxide have been used for base materials composed of glass or silicon (for example, Non-Patent Literature 1, Non-Patent Literature 2, Patent Literature 3, and Patent Literature 4), a thiol compound for gold-based materials (for example, Non-Patent Literature 3, Patent Literature 4, and Patent Literature 5), and an alkyl phosphoric acid for iron-based or aluminum-based material (Non-patent Literature 4). As seen from the above, it was necessary to select an appropriate compound depending on the material of the base material. For example, it was a fact that a compound, which was effective for base materials such as metal and glass, could not be applicable to a plastic or the like. Other than those above, a polymerization initiating group may be produced by sending radiation or ultraviolet rays to the surface of the base material (for example, Patent Literature 6). Although this method is also applicable to plastic, it has a problem that a portion of the surface of the base material is decomposed and a stable structure cannot be obtained.
Research group of the present inventors worked out earlier a surface-modified base material (polymer coating material precursor) prepared by forming a polydopamine film on a surface of a base material and immobilizing a polymerization initiator on the polydopamine film (Patent Literature 7). This technology is aimed at surface-modified base materials which can coat the surface of the base material with a polymer regardless of the material of the base material. It also undergo a two-step reaction of preparing the polydopamine film over time by oxidative polymerization of a dopamine solution at room temperature and then further immobilizing the initiator. Thus, it has a disadvantage of requiring long preparation time and being cumbersome. The technology described in Patent Literature 7 made an attempt to confirm applicability to base materials which are composed of silicon, metals such as aluminum and stainless steel, and plastic such as PTFE, but has not confirmed applicability to other plastics, for example, thermosetting resin such as phenol resin known for difficult modification.